Memcached::cas

Description

Memcached::cas() performs a "check and set" operation,
so that the item will be stored only if no other client has updated it
since it was last fetched by this client. The check is done via the
cas_token parameter which is a unique 64-bit
value assigned to the existing item by memcache. See the documentation for
Memcached::get*() methods for how to obtain this
token. Note that the token is represented as a double due to the
limitations of PHP's integer space.

Parameters

cas_token

Unique value associated with the existing item. Generated by memcache.

See Also

User Contributed Notes 4 notes

When using binary protocol, the expected result after cas() is 21 (Memcached::RES_END).

For example, to make the above example #1 work with binary protocol, use the following:
<?php
$m = new Memcached();
$m->addServer('localhost', 11211);
$m->setOption(Memcached::OPT_BINARY_PROTOCOL,true)

I'm not sure whether this remains true in the newer versions of the Memcached module (v3.0 onwards) but in the version shipped with PHP 5.6 the return value and result code when using this method with OPT_BINARY_PROTOCOL enabled are entirely useless.

Setting a value successful may return true, with a result code of RES_END, but it may also return true with a result code of RES_SUCCESS.

However, *unsuccessfully* setting a value likewise seems to return true and RES_SUCCESS, effectively rendering this function's return value useless with the binary protocol enabled as it is impossible to distinguish success from failure.

If you need to rely on the return value of this method then I strongly recommend disabling the binary protocol under PHP 5.6, as in its current state the common memcached module is too broken otherwise for CAS usage.

Hopefully someone else can weigh in on whether this is still broken in newer versions or not.